<%@ page contentType="image/jpeg"
	import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*"
	pageEncoding="GBK"%>
<%!Color getRandColor(int fc, int bc) {//给定范围获得随机颜色
		Random random = new Random();
		if (fc > 255)
			fc = 255;
		if (bc > 255)
			bc = 255;
		int r = fc + random.nextInt(bc - fc);
		int g = fc + random.nextInt(bc - fc);
		int b = fc + random.nextInt(bc - fc);
		return new Color(r, g, b);
	}%>
<%
	//设置页面不缓存
	response.setHeader("Pragma", "No-cache");
	response.setHeader("Cache-Control", "no-cache");
	response.setDateHeader("Expires", 0);

	// 在内存中创建图象
	// 通过这里可以修改图片大小
	int width = 85, height = 23;
	BufferedImage image = new BufferedImage(width, height,
			BufferedImage.TYPE_INT_RGB);
	Graphics g = image.getGraphics();
	Random random = new Random();

	g.setColor(getRandColor(200, 250));
	g.fillRect(0, 0, width, height);
	
	//设定字体
	g.setFont(new Font("黑体", Font.PLAIN, 18));

	//画边框
	g.setColor(Color.BLUE);
	g.drawRect(0,0,width-1,height-1);

	// 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
	g.setColor(getRandColor(160, 200));
	for (int i = 0; i < 155; i++) {
		int x = random.nextInt(width);
		int y = random.nextInt(height);
		int xl = random.nextInt(12);
		int yl = random.nextInt(12);
		g.drawLine(x, y, x + xl, y + yl);
	}

	String sRand = "";
	// 如果要使用中文，必须定义字库，可以使用数组进行定义
	// 这里直接写中文会出乱码，必须将中文转换为unicode编码
	String[] str = { "A", "B", "C", "D", "E", "F", "G", "H", "J", "K",
			"L", "M", "N", "P", "Q", "R", "S", "T", "U", "V", "W", "X",
			"Y", "Z", "a", "b", "c", "d", "e", "f", "g", "h", "i", "j",
			"k", "m", "n", "p", "s", "t", "u", "v", "w", "x", "y", "z",
			"1", "2", "3", "4", "5", "6", "7", "8", "9" };

	for (int i = 0; i < 5; i++) {
		String rand = str[random.nextInt(str.length)];
		sRand += rand;
		// 将认证码显示到图象中
		g.setColor(new Color(20 + random.nextInt(110), 20 + random
				.nextInt(110), 20 + random.nextInt(110)));//调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
		g.drawString(rand, 16 * i + 6, 19);
	}

	// 将认证码存入SESSION
	session.setAttribute("rand", sRand);
	// 图象生效
	g.dispose();
	// 输出图象到页面
	ImageIO.write(image, "JPEG", response.getOutputStream());
	out.clear();
	out = pageContext.pushBody();
%>